1. Field of Invention:
This invention relates generally to athletic shoes, and more particularly to a shoe that is so insulated as to minimize heating of a foot housed therein as a result of solar radiation and heat conduction from the ground, and which is so ventilated as to draw into the shoe interior relatively cool ambient air and to discharge therefrom moist and warm air developed as a result of athletic activity, whereby the foot is maintained in a relatively dry and cool state.
2. Status of Prior Art:
Because of exertions involved in sports activities such as running and jogging, a wearer of athletic shoes is subjected to the adverse effects of the moist and relatively warm air developed within the interior of the shoe as a result of perspiration and heat. Thus marathon racing tests have shown that when the ambient temperature is about 80.degree. F., the internal shoe temperature in some instances exceeds 110.degree. F. Shoes which are hot and moist are not conducive to athletic activity nor are they beneficial to the feet. And apart from the fact that shoes are rendered uncomfortable by internally-developed moist and warm air having a high salt content, this vapor attacks the materials from which the shoes are fabricated and shortens their effective life.
The transfer of heat takes place by three processes: conduction, convection and radiation. In conduction, heat is transferred through a body by the short range interaction of molecules and/or electrons. Convection involves the transfer of heat by the combined mechanisms of fluid mixing and conduction. In radiation, electromagnetic energy is emitted toward a body and the energy incident thereto is absorbed by the body to raise its temperature. Radiant heating, therefore, differs from both convection and conduction heating, for the presence of matter is not required for the transmission of radiant energy.
In conduction and convection heating, the rate of heat transfer is proportional only to the temperature difference between the body being heated and the surrounding transfer medium; hence such heating is relatively slow as compared to the nearly instantaneous effect of radiant heating.
An athletic shoe is subjected to heat build-up and rendered uncomfortable because of heat arising from three distinct sources. The first is heat resulting from exposure of the shoe to incident solar radiation. The extent to which radiant heat presents a problem depends, of course, upon where the athletic activity is being carried out. On a sunny day, solar radiation may be a significant factor.
The second source is ground heat conducted to the shoe interior through the sole of the foot. Such ground het, in some instances, particularly when the wearer is running on a hard, paved surface exposed to the sun, may lead to a heavy heat build-up, thereby causing profuse perspiration on the part of the wearer. The third source of heat is a result of internal friction when the housed foot rubs against the inner liner of the shoe. Where an athletic shoe makes use of flexible foam rubber or plastic materials for the inner and outer soles as well as the inner liner, because of the heat insulating capacities of these materials, they contribute to heat build-up.
The idea of incorporating ventilating means in a shoe to introduce cooling air therein appears repeatedly in the prior art. Thus the patent to Marabini, U.S. Pat. No. 1,225,455, shows a shoe having an elastic tube therein to compress air drawn from the exterior and to force this air into the shoe interior.
The Brahm patent U.S. Pat. No. 3,475,836 provides an air pumping action in a shoe, air being drawn through a valve and being forced out of openings. Similar pneumatic pumping schemes are shown in Estandian, U.S. Pat. Nos. 3,315,379, in Karras, 3,331,146, El Sakkaff, 4,602,441 and Lee, 4,654,982.
The incorporation of air scoops in shoes to pick up air and feed the air into the shoe interior is found in Berlese, U.S. Pat. Nos. 4,679,335; Dassler, 4,100,685; Kim, 4,224,746; Inohara, 4,359,830; McBarron, 4,438,573 and Sakutori, 4,445,284. Also of interest in regard to shoe ventilation are the patents to Doak, U.S. Pat. Nos. 4,397,104; Fukuoka, 4,468,869 and Stec, 3,335,505.
While the prior art provides various expedients to effect shoe ventilation, the means for this purpose are relatively inefficient, for they fail to separate the hot and moist air developed within the shoe interior from the incoming cool air, so that it is not mainly the damp air which is discharged. Also, the prior art does not take into account the effect of solar radiation and ground heat on heat build-up within the shoe.